Signal system



w. P. PLACE SIGNAL SYSTEM April 16,` 1940.

Filed Nov. 8, 1938 SSR AGN

HIS ATTORNEY oR lace.

16, 1940. w, P, PLACE 2,197,415

SIGNAL SYSTEM Filed Nov. 8,1938 4 sheets-sheet 2 T? VT? v HIS ATTORNEY April 16, 1940. w. P. PLACE l -2,197,415

SIGNAL SYSTEM Filed Nov. 8, 1938 4 Sheets-Sheet 5 HIS ATTORNEY Secand Fig. 9.

April 16, 1940. w. P. PLACE vSIGNAL. SYSTEM Filed Nov. 8, 1958 4 Sheets-Sheet 4 IQ/Ce.

ATTORNEY HIS Patented Apr. 16, 1940 UNITED STATES PATENT OFFICEg SIGNAL SYSTEM Application November 8, 1938, Serial No. 239,523

24 Claims.

My invention relates to signal systems, and more specically to signal systems for railways.

I shall describe several forms of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

f A feature of my invention is the provision in signal systems of the type here involved of novel and improved means selectively responsive to code current impulses. Another feature of my invention is the provision in signal systems of the type here contemplated of novel and improved means for prolonging the eiects of a current impulse so that a relay or other electromagnetic device, which requires a relatively long interval for the building up of proper energization, is effectively energized in response to a current impulse of relatively short duration. When apparatus embodying my invention is used for railway signal systems, another feature of the invention is the provision of novel and improved means to provide substantially the same average energization of a track relay under all Weather conditions, to increase the shunting sensitivity of a track circuit, and to provide when a track u circuit is occupied by a train current surges of relatively high amperage as an aid in energy transfer between the track rails and train carried signal apparatus. Other features and advantages of my invention will appear as the specification' progresses.

In the accompanying drawings, Figs. 1 and 2 when taken together are diagrammatic viewsof one form of apparatus embodying my invention when used with a railway signal system, Fig. l being the trackway portion of the apparatus and Fig. 2 being the train carried portion of the apparatus. Fig. 3 is a diagrammatic view` of a modied form of the train carried apparatus of Fig. 2 which also embodies my invention. Figs. 4 and 5 when takentogether are diagrammatic views of another form of apparatus embodying my invention when applied to a railway signal system, Fig. 4 being the trackway portion of the apparatus and Fig. 5fbeing the train carried portion of the apparatus. Fig.6 is a diagrammatic view of a modicatlon of the train carried apparatus of Fig. 5 which also embodies the invention` Figs. 7 and 8 are diagrams illustrating operating characteristics of the trackway appa- 55 Figs. 5 and 6.

ratus of Fig. l and Fig. 4. Figs. 9 and 10 are Similar parts are identied by like reference characters in each of the several views.

It is to be understood that I do not Wish to limit my invention to signal Systems for railways, and this one use will serve as an illustration of 5 the many places where the apparatus is useful. Referring to Fig. 1, the reference characters la and Ib designatey the trac rails of a railway over which traffic normally moves in the direction indicated by an arrow and which is formed by 10 the usual insulated rail joints into consecutive track sections for signaling, a Single section W-X and the adjoining ends of the two sections adjacent, thereto only being shown for the sake of simplicity. Each track section isuprovided with a track circuit which comprises a source of coded current connected across the track rails at the exit end of the section and a receiving and decoding relay means connected across the rails at the entrance of the section. Looking at sec- 20 tion W-X, the source of coded current comprises a battery Z, a code transmitter C `and a reactance device RX.v The connections of battery 2 are controlled by a control relay XH to be later described, the contact fingers 3 and 4 of relay -XII serving to pole 'change the connections of battery r2 as will be readily understood by an inspection of Fig. 1. V y

The code transmitter C50 may be any one of several well-known types, and as here shown is of the relay type, the operating winding of which is permanently connected across a source of current whose terminals are Band C. yHence the code transmitter C50 is continuously energized to operate a code contact member 50 at a selected rate which may be, for example, 50 operations per minute. That is to say,jthe code transmitter C50 divides time into successive operation cycles of a selected interval each, the contact member 50 being operated once each cycle to break engagement with a stationary Contact 50a.

` 'I'he reactance device RX includes an inductor or transformer winding 5 and a condenser 6. 'I'he condenser vli is connected'across the winding 5 and the two in multiple are connected across the battery 2 over code Contact member 50 and the pole changing contact fingers 3 and 4 of relay XH. The winding 5 is provided with taps and a selected portion of the winding is connected across the track rails over wires 1 and 8. The condenser 6 is preferably of relatively large capacity, and the parts are so proportioned that the circuit thus formed by the track rails and the reactance device isan oscillatory circuit, the

frequency or oscillation period of which is largely determined by the condenser 8 and inductor 5 and is determined to a small degree by the ballast resistance.

When relay XH is energized in a manner to appear later, current of one polarity is supplied to the reactance device during the period the code Contact member 50 engages contact 50a, and energy is stored in the magnetic circuit of winding 5 and condenser 6 is charged. The parts are preferably so designed with respect to the time constant of the circuit and with respect to the manner of closing contact SII- 50c that energy in the reactance device RX builds up rather slowly and no energy is transferred to the track rails during the storing of the energy in the reactance device, or at least the magnitude of the energy transferred to the rails at this time is so small that it can be neglected. Each time code contact member 5D breaks engagement with contact 5M, the magnetic energy causes a high voltage to ce impressed across the terminals of condenser 6 and by transformer action a proportional voltage to be impressed across the track by way of wires 'I and 8. The condenser B and inductance of winding 5 form an oscillatory circuit damped by the ballast resistance of the track, and a current impulse is transferred to the track rails, the current impulse having a damped wave by virtue of the oscillatory nature of the circuit. Under wet wea-ther conditions and the ballast resistance is low, the oscillations are highly damped, and as illustrated in Fig. 7 the current wave consists of substantially onehalf cycle only. Under dry weather conditions, the ballast resistance is relatively high and the oscillations persist for several cycles before dying out. As illustrated in Fig. 8, the amplitude of each half cycle is materially larger than the amplitude of the half cycle immediately following it. The result of such current impulse and wave form therefore is that the average energization of a relay connected across the rails at the entrance of the section during dry Weather conditions is about equal to the average energization of the relay during wet weather conditions. It is to be observed from Figs. 7 and 8 that in any event the first half cycle of the wave form is the dominating half cycle. This rst halt cycle is of relatively high peak voltage and high shunting sensitivity of the track circuit is provided because the high peak voltage of the rst half cycle of each current impulse aids in breaking down the lm resistance of the track rails. Because of the high peak voltage of the rst half cycle of each current impulse, a current surge of relatively high amperage is produced when the track rails are shunted by a train. Such high amperage of current, together with the short duration of the impulse, results .in a relatively high energy transfer being effected inductively between the rails and inductors mounted on the train. As illustrated in Figs. 'l' and 8, the duration of the current impulse is only a small portion of the operation cycle interval of the code transmitter. Taking the cycle interval to be, as here assiuned for the purpose of illustration, 1.2 seconds each or 50 cycles per minute, the first half cycle of the Wave may be, for example, of the order of .O05 second. Consequently, the energy output required of the battery 2 can be made relatively small.

When the control relay XH is released, the action is similar except the current impulse supplied to the track circuit is opposite in polarity to that supplied when the relay XH is picked up. To aid in understanding the invention, I shall assume the connections are such that with relay XH picked up, the first half cycle of each current impulse supplied to the track circuit is of positive polarity so that the rail Ia is positive and the rail Ib is negative. When the relay XH is released, the rst half cycle of each current impulse supplied to the track circuit is of negative polarity, and rail Ib is positive and rail Ia is negative. It follows, therefore, that the track circuit for section W-X is supplied with current of the polarity code type, the frequency of the impulses being the same under each code, and being, as here assumed for the purpose of illustration, 5G cycles per minute. From the foregoing description it is to be seen that the coded current impulses supplied to the track rails effect .ubstantially the same average energization of the track relay under all weather conditions. Aso, the rst half cycle of the damped Wave of each current impulse is of relatively high peak voltage and high shunting sensitivity of the track circuit is assured. Because the rst half cycle is of relatively high peak voltage and short duration, correspondingly high energy transfer is effected between the rails and train carried apparatus to be later described. Since each current impulse persists for only a small portion of each operating cycle, the energy consumed from the battery 2 can be made relatively low.

The receiving and decoding relay means connected across the rails of the entrance of section W-X include two code following relays CFI and CF2, two decoding relays SI and S2, and two condensers CI and C2.

The code following relays CFI and CF2 are preferably of the quick acting polar type. The operating windings of relays CFI and CF2 are connected in multiple across the track rails but with opposite polarity. That is, the left-hand terminal of the winding of the relay CFI and the right-hand terminal of the winding of relay CF2 are connected with the rail I a, while the righthand terminal of the winding of relay CFI and the left-hand terminal of the winding of relay CF2 are connected with rail Ib. The relays CFI and CF2 are provided with polar conta-ct members 9 and I2, respectively, and these polar contact members are biased to seek a selected position when the winding of the relay is deenergized. Thus polar contact member 9 of relay CFI seeks under the influence of the bias the left-hand position, closing normal polar contact 9-I0 when the relay is deenerglzed, is retained at the same left-hand position when the relay is energized by current owlng through the winding of the relay from the right-hand terminal to the left-hand terminal, and the contact member 9 is operated to the right-hand position, closing reverse polar contact 9--II when the relay winding is energized by current flowing from the left-hand terminal to the right-hand terminal. The polar contact member I2 of relay CF2 seeks under the influence of its bias the left-hand position. closing normal polar contact I2-I3, is retained at this left-hand position when the relay is energized by current flowing in its winding from the right-hand terminal to the left-hand terminal, and is operated to the right-hand position closing reverse polar contact I Z-Il when the relay is energized by current flowing in its winding from the left-hand to the right-hanf' terminal.

It follows that when a current impulse of positive polarity is supplied to the track rails of sec? tion W-X and rail Ia is positive and rail Ib is negative, the relay CFI is operated and relay CF2 remains inactive. When a current impulse of negative polarity is supplied to the track rails and rail Ib is positive and rail Ia is negative, the relay CF2 is operated and relay CFI remains inactive. Since the duration of each current impulse supplied to the rails of section W-X is relatively short and the impulse persists for only a small portion of the operating cycle into which time is divided by the code transmitter, the period the contact member 9 or I2 is held at the right-hand position when the respective relay is operated, is short, and is only a small fractiony of the time the contact member 9 or I2 is held at the left-hand position. Furthermore, it is to be observed that when the current impulseis of positive polarity the relay CF2 is energized during the first half cycle at a polarity which tends to retain the polar contact member I2 at its biased or left-hand position. The second half cycle of the current impulse tends to energize relay CF2 at a polarity to operate the contact member I2. However, the magnetic iield built up in the relay CF2 during the first half cycle of the current impulse is relatively large and, because the duration of the second half cycle is short, the magnetic field built up during the rst half cycle does not die away to zero and build up in the opposite direction to any extent and hence the net effect is that the contact member I2 remains firmly held at its biased position. In other words, the resultant energization of relay CF2, when the track circuit current impulse is of positive polarity, is of the polarity that causes contact member I2 to remain under the influence of its bias. When the track circuit current is of negative polarity, the action with respect to relay CFI is similar to that just described for relay CF2 when the track circuit current impulse is of positive polarity. That is, the resultant energization of relay CFI, when the track circuit current impulse is of negative polarity, is of the polarity that causes its contact member 9 to remain under the influence of its bias.

Decoding relays SI and S2 are preferably neutra] relays provided with slow release characteristics, relay SI being controlled by code following relay CFI through the medium of the condenser CI, and relay S2 being controlled bycode following relay CF2 through the medium of the condenser C2. When relay CFI is operated, closing its reverse polar contact 9-I I, the condenser CI is connected across the B and C terminals of a convenient source of direct current (not shown) and the condenser is charged. When relay CFI closes its normal polar contact 9-I0, condenser CI is connected across the winding of relay SI and discharges to energize relay SI. Hence, when relay CFI is periodically operated at` the code frequency of cycles per minute, condenser CI is charged each time contact 9-II is closed' and discharges through the winding of relay SI each time contact 9-I0 is closed,

with the result that relay SI is energized and picked up, and is retained picked up due to its slow release characteristics. Likewise, when relay CFZ is operated closing its contact I2-I4, the condenser C2 is connected across the terminals B and C` of t-he current source and is charged. Condenser C2 then discharges through the winding of relay S2 to energize that relay when contact I2--I3 of the code following relay CF2 is closed. With relay `CF2 operated at the code frequency of 50 cycles per minute, the condenser C2 is charged each time contact I2-I4 is closed and discharges through the winding of relay S2 each time contact I2-I3 is closed, with the result that relay S2 is energized and picked up and is retained picked up by virtue of its slow release period.

As stated above, the interval the relay CFI or CF2 is operated to close reverse polar contact 9-II or I2-I4 is short due to the sho-rt duration oi the track circuit current impulse, but such interval is sufflicent to charge condenser CI or C2. During the relatively long remaining portion of each cycle interval the condenser CI or C2 is connected with the winding of the decoding relay SI `or S2, with the result that the energizing of relay SI orSZ is of ample duration to pick up that relay, whereas the duration of the current` impulse of the track circuit current, while suiiicient to operate the quick acting polar relay CFI or CF2,'miglit not be sufficient toI properly energize the slow acting electromagnetic device or relay SI or S2. In other words, the receiving and decoding `relay means of section W-X is operative to effect in response to a current impulse of short duration a relatively long period of energization of the slow acting decoding relay.

Decoding relays SI and S2 are used to control the' operating circuits of a wayside'signal SW for section W-X, vand to govern a control relay WHS, which latter relay governs the connections ofwbattery 2 for the track circuit of the track section next 4in the rear of section W-X in the same manner that relay XH controls the conn nections of battery 2 for the track circuit of section W-X Furthermore, relay XH is governed by the decoding, relays (not shown) :for the track circuit for the section next in advance of section W-X in the same manner that relay WH is controlled by decoding relays SI and S2. When track section W--X is occupied and its track circuit shunted, vboth code following relays CFI and CF2 are inactive so. that decoding relays SI and S2 are both deenergized and released. The R lamp of signal SW is illuminated over an operating circuit including back contacts I5 and I6 of relays SI and S2, respectively. to display a stop signal indication. Relay WH is now deenergized and the battery 2 for the track circuit of the section next in the rear is connected so as to supply that track circuit with impulses of negative polarity to reflect approach traffic conditions for the section next in the rear because of track section W-X being occupied. When the section next in advance of the section. W-X is occupied and section W-X is unoccupied so that current impulses of negative `polarity areV supplied to the track circuit of section W-X,'

the code following relay CF2 is operated in the manner explained hereinbefore to energize the decoding relay S2. The Y lamp of signal SW is illuminated over an operating circuit including back contact I5 of relay SI and front contact I`I of relay S2 to display an approach signal indication. Relay WH is now energized over front contact I8 of relay S2 and the connection of battery 2 for the track section next in the rear is such that current impulses of positive polarity are supplied to the track circuit of that section to reect clear traffic conditions. When the section next in advance of section W--X and section W-X are both unoccupied and relay XH is picked up'so that current impulses of positive polarity are supplied to the track circuit of section W-X, the code following; relay CFI is operated and the decoding relay SI is picked up but relay S2 is released. The G lamp of signal SW is illuminated over an operating circuit including back Contact i9 of relay S2 and front contact 2li of relay Si to display a clear signal indication. Relay WH is now energized over front contact 2l of relay SI, and current impulses of positive polarity are supplied to the track circuit of the section next in the rear to reiiect clear traflic conditions.

It is to be understood that each track circuit of each section of the railway comprises trackway apparatus similar to that described for the section W-X.

Referring to Fig. 2, the train carried apparatus includes an inductor comprising two windings 22 and 23 mounted on the train in inductive relation with the track rails Ia and Ib, respectively. Windings 22 and 23 are connected across a portion of the winding 24 of an input transformer Tl, the connections of windings 22 and 23 being preferably such that the electromotive forces induced therein by current iiowing in opposite directions in rails Ia and Ib add their effects. The full winding 24 of transformer TI is connected across the grid 25 and filament 26 of an electron tube VTl. a biasing battery 28 being preferably interposed in this grid circuit. The tube VTI is provided with a plate circuit which can be traced from terminal B300 of a generator 29 over primary winding 3G of a coupling transformer T2, plate 3l of tube VTI, tube space to filament 26, and to terminal N300` of generator 29. The generator 22 is driven by any convenient source of power not shown, and supplies a suitable voltage, say, 300 volts.

The secondary winding of coupling transformer T2 is constructed with two portions 32d and 32h which are preferably alike and are connected with the grids of two electron tubes VT2A and VT3 in a push-pull arrangement. The connection of the central terminal of the two portions of the secondary winding 32a-32D is connected with the iilaments of tubes VT2 and VT3 over a biasing battery 38 and an auxiliary biasing unit 35 in series, the unit 35 comprising a resistor 36 and a condenser 3l' in multiple. The plate circuit of tube VT2 includes generator 29 and the winding of a code following relay CFB, and the plate circuit of tube VT3 includes generator 23 and the winding of a code following relay GF4 as will be readily understood by inspection of Fig. 2.

The code following relays CFS and CF4 are preferably of the neutral type and are constructed with quick acting characteristics.

The tubes VT2 and VT3 are normally biased by virtue of biasing battery 38 to practically complete cut-off of plate current. That is to say, when no electromotive force is applied to the grids of tubes VT2 and VT3 through the coupling transformer T2, the biasing of battery 38 renders the grids of tubes VT2 and VT3 negative in potential with respect to the filaments to a degree where the plate current of each tube is substantially Zero.

The code following relays CF3 and GF4 govern two decoding relays R3 and R4` in substantially the same manner the code following relays CFI and CF2 of Fig. 1 govern the associated decoding relays SI and S2. 'When relay CF3 is picked up closing front contact 21. A condenser C3 is charged from a source of direct current whose terminals are B and C, and when the relay CF3 is released closing back contact 33, the condenser C3 discharges through the winding of relay R3 to energize and pick up that relay. Likewise, when relay CF4 is picked up closing front Contact 34, a condenser C4 is charged, and when relay CF4 is released closing back contact 3S, the condenser C4 discharges through the winding of relay R4 to energize and pick up that relay. lays R3 and R4 are slow releasing in character, and hence, when relay CFS or GF4 is operated at the code frequency of 50 cycles per minute, the relay R3 or R4 is retained picked up.

Relays R3 and R4 are used to control the operating circuits of a cab signal CS of the color light type capable of displaying three diiferent indications. The operating circuits for cab signal CS are similar to the circuits for wayside signal SW of Fig. 1, and it is thought the operating circuits of signal CS need no further description.

Assuming the train on which the apparatus of Fig. 2 is mounted is moving in the normal direction of traiiic through the track section W-X of Fig. 1 under clear traific conditions so that code current impulses of positive polarity are supplied to the track circuit, the operation of the apparatus of Fig. 2 is as follows: The first half cycle of each such rail current impulse induces electromotive forces in windings 22 and 23 which add their effects. The wave form of the electromotive force is substantially that illustrated in Fig. 9. That is, the wave form of the induced electromotive force has a iirst half cycle of relatively high peak voltage, while the second half cycle is of relatively low voltage. I have found that under usual operating conditions only the iirst half cycle of the track circuit current impulse induces in the windings 23 and 22 an electromotive force of appreciable amplitude. That is to say, the electromotive force induced in windings 22 and 23 due to the oscillations of the track circuit current impulse other than the iirst half cycle is so small in magnitude that it can be neglected. The electromotive force induced in windings 22 and 23 due to the first half cycle of each current impulse creates in the secondary Winding 32a-32D of transformer T2 an electromotive force of substantially the same wave form, except it is amplified by the tube VTI. The ccnnections are arranged so that the top terminal of secondary winding 32a-32h is rst positive and the lower terminal is negative when the track circuit current impulse is of positive polarity. The grid of tube VT2 is made positive with respect to its filament due to the crest of the wave form. Looking at Fig. 10, the dotted crest portion of the electromotive force wave represents that portion during which the grid of tube VT2 is made positive in potential with respect to the lament of the tube. That is to say, the dotted crest portion of the wave form represents that portion of the induced electromotive force sufcient to overcome the normal bias voltage of battery 38 and the grid of tube VT2 is made positive with respect to its filament. This causes plate current to ow through the tube VT2 and the code following relay CF3 is picked up. Furthermore, this crest voltage causes grid current to iiow in the tube VT2 and condenser 3'I is charged to a voltage equal to the difference between the peak Voltage and the voltage just sufcient to overcome the normal bias voltage of battery 3B. The voltage thus built up on condenser 31 is illustrated by the dotted curve IC of Fig. 10, and increases the normal negative bias on the grid of tube VT3 sothat the immediate negative half cycle of the induced electromotive force which tends to render the grid of tube VT3 positive with respect to its filament is canceled and no current flows in the plate circuit of tube VT3. The charge on condenser 31 leaks away through resistor 36 during the interval between successive impulses so that the above described operation of the apparatus is repeated each impulse o1 the track circuit current.

It is to be noted that device 35 enables tubes VT2 and VT3 to operate properly over a wide range of track current. If the crest voltage of the first half cycle is only sufficiently strong to cause, say, VT2 to operate relay CF3 but not sufciently strong to cause grid current to flow, the immediately following half cycle is not strong enough to cause VT3 to operate CF4 and no increased bias is needed. If the voltage is considerably higher, a higher voltage is built up across the terminals of condenser 31, the immediate negative half cycle is cancelled, and no plate current flows in tube VT3.

It follows that the code following relay CF3 is operated at a rate corresponding to the code frequency of the track circuit current impulses. The period the relay CF3 is picked up to close front contact 21 is short but is suicient to charge condenser C3, which condenser then by discharging through the winding of relay R3 over the back contact 33 of relay CF3 causes relay R3 to be energized for a sulcient interval to pick up that relay. Relay R3 is retained picked up from one impulse to the next by virtue of its slow release period. Hence the impulse which operates the code following relay CF3 is in effect prolonged sufflciently to operate the decoding relay R3. n

With the decoding relay R3 picked up closing front contact 40, the G lamp of the cab signal CS is illuminated to display a clear signal indication.

With approach trafiic conditions existing while the train occupies the track section W-X, the code current impulses of the track circuit are of negative polarity and the electromotive force induced in windings 22 and 23 is of opposite polarity to that induced under clear traffic conditions. 'Ihis time the lower terminal of the secondary winding 32a-32h is first positive and the upper terminal is negative so that the grid of the tube VT3 is made positive in potential with respect to the filament of that tube during the upper crest portion of the wave form of the induced electromotive force. Plate current flows for the tube VT3 and the code following relay CF4 is operated. Condenser 3l is charged in the same manner as described before and increases the negative grid bias of tube VT2 so that the immediate following half cycle of the induced electromotive force which tends to render the grid of tube VT2 positive is canceled and no plate current flows for the tube VT2. Hence relay CF4 is picked up each current impulse of the track circuit current and relay R4 is energized because the condenser C4 is charged during the brief interval the front contact 34 of relay CF4 is closed and then discharges through the winding of relay R4 during the longer interval the back contact 39 of relay CF4 is closed. With relay R4 picked up closing front contact 4| and relay R3 released closing back contact 42, the Y lamp of cab signal CS is illuminated to display an approach signal indication.

If the track section W-X is already occupied -ondary windings 48 and 49. -proportioned that the wave form ofthe electroby a train when 'the train on which the apparatus of Fig. 2 is mounted enters that track section, no electromotive force is induced in the windings 22 and 23 and both code following relays CF3 andY CF4 are inactive so that the decoding relays R3 and R4 are deenergized and released. The R lamp of signal CS is now illuminated over a circuit including back contacts 42 and 43 of relays R3 and R4, respectively, to display a slow speed cab signal indication.

In the train carried apparatus of Fig. 3, the winding 24 of the input transformer 'll is connected across grid 44 and filament 45 of an electron tube VT4, a biasing battery 46 being preferably interposed in the circuit. The plate circuit ior tube VT4 includes generator 29 and the primary winding 4l of an output transformer T3, transformer T3 being provided with two secondary windings 48 and 49. Winding 48 is connected with the winding of a code following relay CFS, and winding 49 is connected with the Winding of a code following relay CFB. The code following relays CFS and CFG are preferably of the quick acting polar type having polar contact members biased to seek a selected position when the relay is deenergized similar to the relays CFI and CFZ of Fig. 1. Thus polar contact member 5l of relay CFB seeks its left-hand position when the relay is deenergized, is retained at that position when the relay is energized by current of negative polarity, and is operated to the righthand position when the relay is energizedby current of positive polarity. Contact member 52 of relay CFG is biased to seek its left-hand position when the relay is deenergized, is retained at that position when the relay is energized by current of negative polarity, and is operated to the righthand position when the relay is energized by current of positive polarity.

Decoding relays R3 and R4 of Fig. 3 are governed by the code following relays CFS and CFB, respectively, in substantially the same manner as decoding relays R3 and R4 of Fig. 2 are governed by the associated code following relays CF3 and GF4. That is, condenser C3 is charged when polar contact member 5| of relay CF5 is operated to its right-hand position, closing reverse polar Contact 5I-53, and condenser C3 discharging through the winding of relay R3 to energize relay R3 when normal polar contact 5|-54 of relay CFS is closed, so that operation of relay CFS at the selected code frequency causes decoding relay R3 to be retained picked up. Similarly, condenser C4 is charged when vthe polar contact member 52 of relay CFS is operated to its right-hand position, and condenser C4 discharges through the winding of relay R4 to energize relay R4 when polar contact member 52 is moved back to its left-hand position, so that operation of relayvCFG at the code frequency causes decoding relay R4 to be picked up. Decoding relays R3 and R4 of Fig. 3 govern the operating circuits of the cab signal CS the same as in Fig. 2. l.

In Fig. 3 the parts are so proportioned that tube VT4 is biased to a straight line point of its grid voltage-plate current characteristics, and ay steady value of current normally ows in the plate circuit, which, of course, induces no electromotive forces in the secondary windings 48 and 49. If the grid 44 of tube VT4 is made more positive in potential with respect to filament 45, 'the plate current will increase and such change in the plate current induces electromotive forces in the sec- The parts are so motive force induced in the windings 48 and 49 is in each case substantially that shown in Fig. 9, the rst half cycle of the wave form being of relatively high peak voltage while the second half cycle is of relatively low voltage. If the grid 44 is rendered more negative in potential with respect to filament 45, the plate current is reduced and such reduction of plate current induces electromotive forces in the windings 48 and 49 the same as before, except the electromotive forces are opposite in polarity.

The connections are so arranged that the electromotive force induced in secondary winding 48 when the grid 44 is made more positive and the plate current is increased causes current of posi tive polarity to flow in the winding of relay CFS and that relay is operated. The electromotive force induced in the winding 49 when grid 44 is made more negative in potential and the plate current is reduced causes current of positive polarity to iiow in the winding of relay CFB and that relay is operated. It should be pointed out that the energication of relay CFG, because of the second half cycle of the electromotive force in duced in winding 49 when the plate current is increased, is not sufficient to operate its contact member 52, and likewise the energization of relay CFS, because of the second half cycle of the electromotive force induced in winding 48 when the plate current is reduced, is not sufcient to operate contact member 5l.

Assuming the train on which the apparatus of Fig. 3 is mounted is moving in the normal direction of trafc through the track section W-X of Fig. l under clear traflic conditions, each impulse of the track circuit current of positive polarity induces in windings 22 and 23 an electromotive force which causes the top terminal of winding of transformer Tl to be iirst positive and the bottom terminal of winding 24 to be negative. This causes the grid 44 of tube VT4 to be more positive in potential with respect to lament 45, the plate current is increased and relay OF5 is operated sc that decoding relay R3 is picked up, and a clear cab signal indication is displayed by the signal CS. If approach trac conditions exist for the track section 'VV-X, then each current impulse of the track circuit is of negative polarity and the electromotive force induced in the windings 22 and 23 of Fig. 3 causes the lower terminal of winding 2d to be positive and the top terminal to be negative. This time the grid 44 is made more negative in potential with respect to lilament 45, the plate current is reduced, and relay CFS is operated so that decoding relay R4 is picked up and an approach cab signal is displayed. If the track section W-X is already occupied when the train on which the apparatus oi Fig. 3 is mounted enters section W-X, then no electromotive force is induced in the windings 22 and 23, both relays CFE and CFE are inactive, and both decoding relays R3 and R4 are released so that a. slow speed cab signal indication is displayed.

Referring to Fig. 4, the track rails I a and Ib of a railway over which trailic normally moves in the direction indicated by an arrow are formed into consecutive track sections the same as in Fig. l, a single section W--X and the ends of the adjacent sections only being shown. In Fig. 4 the track section W-X is provided with a socalled cut section subdividing the section into two subsections W--V and V--X.

Each track section of Fig. 4 is provided with a track circuit the sanle as in Fig. 1. The track circuit for section W-X of 4 comprises a source of coded current connected across the rails at the exit of the section and a receiving and decoding relay means connected across the rails at the entrance of the section, the same in Fig. l, and includes in addition a code repeating means connected across the rails at the cut section location V. In Fig. 4 the trackway apparatus is adaptable of supplying coded current of four different codes for a four block iive indication signal system.

Looking at the exit of the section W--X of Fig. 4, the source of coded current comprises a battery 2, two code transmitters C50 and C15, and reactance device RX. The code transmitter C15 is preferably the same as code transmitter C50 except it is adjusted to operate its code contact member 15 at the code frequency of 75 operations per minute, whereas the code transmitter C50 operates its code contact member 50 at the code frequency of 50 cycles per minute. The reactance device RX of Fig. 4 comprises inductor winding 5 and a condenser 6 the same as in Fig. l, and a selected portion of winding 5 is connected across the rails la and il) over wires 1 and 8. The connection of battery 2 is pole changed by control relay XH the same as in Fig. l, while selection between the code transmitter C50 and code transmitter C15 is made by a second control relay XHI.

When both relays XH and XH! are picked up in a manner to appear later to reflect clear traiiic conditions for section VV-X, the track rails of subsection V-X are supplied with a current irnpulse of positive polarity each time the code transmitter C15 operates its contact member 15 to break engagement with contact 15a, the current impulse having a damped wave the same as explained in connection with Fig. l. Hence the iirst half cycle of the current impulse iiowing in the track rails of subsection V-X is of positive polarity and the current impulses have a code frequency of cycles per minute.

When control relay XH is released and control relay XHI is picked up to reflect approach restricting trailic conditions for the section W-X, as will shortly appear, the current impulses supplied to the rails of subsection V-X are of negative polarity and of the '75 code frequency. When both relays XH and XHI are released 'to reect approach traffic conditions ior the section W-X, the track rails of subsection V--X are supplied with current impulses of negative polarity at the code frequency of 50 cycles per minute. Again, when relay XH is picked up and relay XHI is released to reflect restricting traflic conditions for the section W-X, the 'track rails of subsec tion V-X are supplied with current impulses of positive polarity at the code frequency of 50 cycles per minute. The stop or slow speed traiiic condition for section W-X is reflected when the track circuit is shunted. Preferably the full winding 5 of reactance device RX is used when the code transmitter C58 is active, while only a portion of the winding is used when the code transmitter C15 is active.

The code repeating means at location V includes a battery 2a, two code following relays CFI and CF2, a control relay VH, and a reactance device RV. Relays CFI and CF2 are preferably quick acting polar relays the same as in Fig. l, the windings of the two relays being connected across therails of the subsection V--X in multiple and theconnections being so arranged that relay CFI is operated by current impulses of positive polarity and,v relay CF2 is operated by current impulses of negative polarity. The control relay VH is controlled over a polar contact member 51 of relay CFI through the medium of a'condenser rC1 as will be understood by an inspection of Fig. 4. The reactance device RV is substantially the same as the reactance device RX and is provided with a winding 58 and a condenser 60 of relatively large capacity. A selected portion of winding 58 is connected across the rails of subsection W-V. The connections of battery 2a with the reactance device RV are pole changed by contact fingers 55 and 56 of relay VH and are governed by polar Contact members 9 and I2 of relays CFI and CF2, respectively.

When clear traflic conditions exist for the section W-X and current impulses of positive polar- -ity and of a 75 code frequencyA are supplied to the rails at location X, the code following relay CFI at location V is operated at the same frequency and relay VH is picked up. With relay VH picked up and contact member 9 of relay CFI operated at the code frequency of '75, current impulses of positive polarity and of the 75 code frequency are supplied to the rails of subsection W-V. That is to say, the code of the current impulses flowing in the rails of subsection V-X is repeated for the current impulses supplied to the rails of the subsection W-V. Under approach restricting traffic conditions for the section W-X and current impulses of negative polarity and 75 code frequency are supplied to the rails at location X, the code following relay CF2 is operated at the corresponding code frequency, control relay VH being now deenergized and released. With relay VH released and contact member I2 operated at the code frequency of 75 cycles per minute, current impulses of negative polarity and the code frequency of 75 are supplied to the rails of the subsection W-V. Under approach traffic conditions and current impulses of negative polarity and of the 50 code frequency are supplied to the railsk at location X, the code following relay CF2 is operated at the corresponding code frequency, relay VH is released and the current impulses supplied to the rails of subsection W-V are of negative polarity and of the code frequency of 50 cycles per minute. Under restricting traflic conditions and code impulses of positive polarity and of 50 cycles per minute are supplied to the rails at location X, the relay CFI is operated and control relay VH is picked up, with the result that this code is repeated for the current impulses supplied to the rails of subsection W-V. If the subsection V-X is occupied, both code following relays CFI and CF2 are inactive and no currentimpulses are supplied to the rails of the subsection W-V.

'I'he receiving and decoding means of Fig. 4 comprises two code following relays CF1 and CFS, two decoding transformers T1 and T8, and four decoding relays S3, S4, S5 and S6.

The code following relays CF1 and CFB are preferably biased polar relays similar to relays CFI and CF2, except relays CF1 and CFB are each provided with a lower or holding winding and have associated therewith condensers C5 and C6, respectively, for equalizing the on and off" periods of the relay in order to provide sumcient time when relay CF1 or CFB is operated for the associated decoding relays to be effectively energized. The relays CF1 and CF8 have their top or operating windings connected in multiple across the track rails at reversed polarity, the arrangement being such that relay CF1 is operated by track circuit current impulses of positive polarity and relay CFB is operated by current impulses of negative polarity.

Normally the condenser C5 is charged from a direct current source over normal polar contact 6I62 of relay CF1, and discharges through the holding winding of relay CF1 when that relay is operated, closing its reverse polar contact lil-63. This discharge of condenser C5 acts to retain relay CF1 at its operated position for an appreciable instant after the impulse of current which operated the relay ceases to flow in the operating Winding of the relay. Similarly, condenser C6 is normally charged and discharges through the holding winding of relay CFB when that relay is operated to retain the relay in its operated position for an appreciable instant after the impulse which operated the ,relay ceases to flow in the operating winding of relay CF8. The charge built up in condenser C5 or C6 when connected across the source of direct current depends upon the interval the connection is completed and also upon the resistor I21 or I28 interposed in the respective connections. When the code frequency for the current impulses is 75 cycles per minute, the interval between successive current impulses and during which interval the relay CF1 or CFB is retained at its biased position, isy of a correspondingly short interval. Consequently the condenser C5 or C6 acquires only a relatively small charge and the subsequent discharge through the holding Winding of relay CF1 or CFB is elective to hold that relay at its operated postion for only a corresponding interval.

On the other hand, if the code frequency for the current impulses is 50` cycles per minute, condenser C5 or C8 acquires a greater charge and the subsequent discharge through the holding winding of the associated relay is effective to hold that relay at its operated position for a correspondingly longer interval. By properly proportioning the parts, the time during which relays CF1 and CFS are retained at their operating position (on period) can be made approximately equal to the time the relays are retained at their biased position (off period) for both the 50 and 75 code frequencies.

When relay CF1 is operated, direct current is reversibly supplied over polar contact member 64 toy two portions of primary winding 65 of the decoding transformer T1. A secondary winding 66 of transformer T1 is connected with the winding of relay S5 through a full wave rectifier 61. A portion of winding 65 of transformer T1 is connected with the winding of relay S6 through a rectifier 69 and a lter comprising a condenser V1li and a transformer 68. The filter including condenser 10 and transformer 68 is proportioned to pass electromotive forces of the frequency corresponding to the 75 code frequencyof the track circuit current impulses. Hence, when relay CF1 is operated at either the 50 or 75 code frequency, relay S5 is picked up, and, when relay CF1 is operated at the code frequency of 75, the relay S6 is also picked up. In like fashion, relay CFB reversibly applies direct current over its polar contactmember 1I to two portions of the primary winding 12 of decoding transformer T8. A secondary winding 13 of transformer T8 is connected with the winding of relay S3 through a full wave rectifier 14. A portion of winding 12 is connected with the winding of relay S4 through a full wave rectifier 16 and a filter comprising a condenser 11 and a transformer 18. The filter including condenser 11 and transformer 18 is proportioned to pass electromotive forces of the frequency corlows that when relay CF8 is operated at either the or 50 code frequency relay S3 is picked up and relay is also picked up when the relay is operated at the 'l5 code frequency.

The relays S3, Sil, S5 and SS are used to control the operating circuits of a wayside signal SW2' which in Fig. a is shown as a color light signal capable ci' displaying five different indications. The relays S3, S4, S5 and SE are also used to govern two control relays WH and WHI, which latter relays in turn control the track circuit for the section next in the rear of section W-X in the same manner that relays XH and XH! control the track circuit for the section W-X. Furthermore, relays XH and XHl are governed by the decoding relays (not shown) for the track section next in advance of section W-X in the same manner that relays WH and WHI are governed by the decoding relays for section W-X.

Under clear tralic conditions for section W-X and the code of the track circuit current impulses is that of positive polarity and 75 cycles per minute, relays S5 and S5 are picked up in the manner explained hereinbefore. Lamp G of the top group of lamps of signal SW| is illuminated over front contacts i5 and Bil of relay S6, and lamp R oi the bottoni group of lamps is illuminated over front contact i9 of relay S5 and front contact 8| of relay S5, and signal SWI displays a green light over a red light :l'or a clear signal indication. Relay WH is now energized over front contact t2 of relay S6, and relay WHI is energized over front contact 82 of relay S5 and front contact 83 of relay S5 so that clear traffic condition is established for the track circuit for the section next in the rear of section W-X.

Under approach restricting trailic conditions and the code for the track circuit current impulses of section vvV-X is that of negative polarity and 'l5 cycles per minute, relays S3 and S4 are picked up in the manner explained hereinbefore. The Y lamp of the top group of lamps oi' signal SWl is illuminated over front Contact or relay Sil, and the G lamp of the bottom Y group of lamps is illuminated over front Contact 85 of relay Sil so that signal SWl displays a yellow lamp over a green lamp for an approach restricting signal indication. Relay WI-Il is noW energized over front contact S6 of relay S3 and relay WH is energized over front contact 81 of relay Sd so that clear traine conditions are still established for the section next in the rear.

Under approach traffic conditions for the section W-X and the code of the track circuit current impulses is that or negative polarity and 50 cycles per minute, the relay S3 is picked up while relays S, S5 and S5 are all released. The Y lamp of the top group of lamps is illuminated as before, while the R lamp of the bottom group ci lamps is illuminated over back contacts 88 and 99 of relays S4 and S5, respectively, and signal SWi displays a yellow light over a red light icr an approach signal indication. Relay WHI is energized over front contact 86 of relay S3 as before but relay WH is deenergized and hence an approach restricting traiic condition is established for the track section next in the rear.

Under restricting trailic conditions and the code for the track circuit current impulses of section W-X is that of positive polarity and 50 cycles per minute, relay S5 is picked up but relays SB, S4 and S5 are released. The R lamp of the top group of lamps is illuminated over back contact 92 of relay S3, front contact 90 of relay S5 and back contact 96 of relay S6, while the Y lamp of the bottom group of lamps is illumihated over back contact 92 of relay S3, front Contact 93 of relay S5 and back contact 94 of relay S5, so that signal SWI displays a red light over a yellow light for a restricting signal indication. Both relays WH and WH! are now released to establish approach tralic conditions for the section next in the rear.

With the track section W-X occupied, both code relays CF1 and CFS are inactive and the associated decoding relays are all deenergized. Under this condition of the relays the R lamp of the top group of lamps is illuminated over back contacts 92, 95 and 96 of relays S3, S5 and S6, respectively, while the R lamp of the bottom group of lamps is illuminated over back contacts 88 and 89 of relays S4 and S5, respectively. Signal SWI now displays a red light over a red light for a stop signal indication. Relay WH is now energized over back contacts 91, and 99 of relays S5, S4 and S3, respectively, while relay WHI is released with the result that restricting trafc condition is established for the section next in the rear.

It will be understood, of course, that the track section W-X of Fig. 4 need not include a cut section and the code following relays CF1 and CFS may be operated directly by the code current impulses supplied to the rails at location X. Furthermore, it will be understood that each track section of the system is provided with trackway apparatus substantially the same as described for section W-X of Fig. 4.

Referring to Fig. 5, the train carried apparatus operatively associated with the trackway apparatus of Fig. 4 includes inductor windings 22 and 23, an input transformer Ti, a iirst stage amplier tube VT|, coupling transformer T2, two amplier tubes VT2 and VTS, code following relays CFS and GF4, decoding transformers T9 and Tl, decoding relays R5, RS, R1 and R8, and a cab signal CSI. The inductor windings 22 and 23, input transformer Tl and the rst stage amplier tubes VTI are the same as in Fig. 2 and need no further description. The grid circuits of tubes VT2 and VTS are connected with the secondary winding 32a-32h of transformer T2, the same as in Fig. 2 except for the fact the biasing battery 38 and auxiliary biasing unit 35 are replaced by two individual control units |00 and |03. In Fig. 5 the control unit |00 comprises a condenser |0| and a resistor |02 in multiple, the control unit |00 being interposed between the grid of tube VT2 and the top terminal of the secondary winding 32a-32h Likewise, the control unit |03 comprises a condenser |05 and a resistor |04, and the control unit |03 is interposed between the grid of tube VT3 and the lower terminal of the secondary winding 32a- 325.

The parts are proportioned so that normally the grids of tubes VT2 and VT3 are substantially of the same potential as the filaments of the tubes, and a relatively large steady iiow of plate current liows to both tubes VT2 and VT3, with the result that the code following relay CF3 interposed in the plate circuit of tube VT2 and the code following relay GF4 interposed in the plate circuit of tube VT3 are both energized and picked up. This operating characteristic of the apparatus of Fig. 5 is illustrated by Fig. l1. The code following relays CF3 and CF4 are neutral relays, the same as in Fig. 2. Relays CF3 and GF4 of Fig. 5 govern the decoding relays R5, R8, R1 and R8 through the medium of decoding transformers T9 and T|0 together with associated lters and rectifiers which are similar to the filters and rectifiers associated with the decoding transformers T'I and T8 of Fig. 4, and it is thought a. description thereof need not be repeated except to point cut that decoding relay R6 is picked up only when code following relay CF4 is operated at the code frequency of '75 cycles per minute, relay R5 is picked up when relay GF4 is operated at either the 50 or 75 code frequency, relay R8 is picked up only when code following relay CF3 is operated at the '75 code frequency, and relay R1 is picked up when relay CF3 is operated at either the 50 or 75 code frequency. 'I'he operating circuits governed by the decoding relays for controlling the cab signal CSI are similar to the operating circuits for signal SWI of Fig. 4 and these operating circuits of Fig. 5 will be described as the operation of the apparatus of Fig. 5 is pointed out.

Assuming the train on which the apparatus of Fig. 5 is mounted is moving in the normal direction of trafilc through the track section W-X of Fig. 4 under clear trafc conditions so that the track circuit is supplied with current impulses of positive polarity and the code frequency of 75, each impulse of track circuit current induces an electromotive force in the windings 22 and 23, which electromotive force is duplicated on an enlarged scale in the secondary windings 32a-32h of transformer T2. The wave form of the electromotive force induced in the secondary windings 32a--32b by each track circuit current impulse is illustrated by the solid line curve of Fig. 12, and this wave form is similar to that illustrated in Fig. 10 in connection with the apparatus of Fig. 2. The connections of transformer T2 of Fig. 5 are so arranged that the top terminal of winding 32a-32h is first positive in potential with respect to the lower terminal during the first half cycle of the induced electromotive force when the track circuit current impulse is of positive polarity. This tends to drive the grid of tube VT2 positive in potential with respect to the filament of that tube, and to drive the grid of tube VT3 negative in potential with respect to the filament of tube VTS. When the grid of tube VT3 is made negative in potential with respect to its filament, the plate circuit of tube VT3 is decreased and the energization of relay CF4 tends to reduce. Since the current impulse lasts for a brief time only (of the order of .005 second), the grid potential returns to zero and the plate current is restored before the code following relay CF4 is released. As stated above, the same half cycle of induced electromotive force drives the grid of tube VT2 positive, so that a grid current flows. This grid current causes a relatively large voltage drop at the control unit |00 comprising resistor |02 and condenser |0|, with the result the grid of tube VT2 is made positive in potential with respect to its filament by only a small amount. Condenser |0| is, however, charged due to the ow of grid current. The plate current of tube VT2 is increased correspondingly when the grid of tube VT2 is driven positive in potential, but this only increases energization of relay CF3. When the half cycle of induced electromotive force ceases, the charge on condenser I0| applies a relatively large negative grid potential to tube VT2, and since the charge on condenser |0| can only leak away through resistor |02 the negative potential of the grid of tube VT2 persists for a relatively long interval. This action of condenser |0| is illustrated by the dotted curve |20 of Fig. 12. The negative grid potential of tube VT2 causes the plate kcurrent to be reduced to a value low enough and for an interval long enough that code following relay CF3 is released. The condenser |0| is fully vdischarged so that the plate current is restored to its normal value and relay CF3 is again picked up before the next impulse of the track circuit current. It follows, therefore, that the above described operation of tube VT2 and the associated code following relay CF3 is repeated for each impulse of the track circuit current, the code following relay CF4 remaining inactive. Operation of relay CF3 at the code frequency of cycles per minute causes relays Rl and R8 to be picked up. By properly proportioning the parts of the control unit |00 and the associated circuits, the interval relay CF3 is released (on period) and the interval relay CF3 is picked up (off period) during each code cycle of track circuit current are substantially equal. In other words, the effect of the current impulse of relatively short duration is prolonged through the medium of the control unit |00 and tube VT2 to provide satisfactory periods for energizing the decoding transformers and relays. Lamp G of the top group of lamps of signal CSI is illuminated over front contacts |06 and |01 of relay R8, and lamp R of the bottom group of lamps is illuminated over front contacts |06 and |08 of relays R8 and R1, respectively, so that signal CSI displays a clear signal indication.

Under approachrestricting trafiic conditions and the current impulses supplied to the track circuit for section W--X are of negative polarity and of the 75 code frequency, the electromotive force produced in the secondary winding 32a-B2b of transformer T2 is opposite in polarity to that described in connection with clear traffic conditions. This time the grid of tube VT3 is made positive in potential with respect to its filament and grid current flows to charge the condenser |05 of the control unit |03. At the termination of the current impulse, condenser |05 discharges slowly through the resistor |04 and provides during this discharge period a negative grid potential for the tube VT3, with the result that the code following relay GF4 is released for an interval. Again, the parts are so proportioned that relay CF4 is operated with substantially each equal on and off period in response to each code cycle of the track circuit current. With relay CF4 operated at the code frequency of '75 cycles per minute, relays R5 and R6 are picked up and relays R1 and R8 are released. The Y lamp of the top group of lamps is illuminated over front contact |09 of relay R5, and the G lamp of the bottom group of lamps is illuminated over front contact ||0 of relay R6 and signal CSI displays an approach restricting signal indication.

Under approach traffic conditions for the track section W-X, the code of the track circuit current is that of negative polarity and 50 cycles per minute. The relay CF4 is operated in response to each current impulse, the same as before, but this time it is operated at the frequency of 50 cycles per minute and only relay R5 is picked up, the relays R6, R1 and R8 being released. The Y lamp of the top group of lamps is now illuminated over front contact |09 of relay R5, and the R lamp of the bottom group of lamps is illuminated over back contacts |I2 and of relays R6 and R1, respectively, so that signal CS| now displays an approach signal indication.

Under restricting traffic conditions for the section W-X the code ci the track circuit current is that of positive polarity and 50 cycles per minutc. Relay CFS is operated in response to each impulse of the track circuit current in the manner explained hereinbefore but at the code frequency of 50 cycles per minute and only relay Rl is picked up, the relays R5, R6 and R8 being released. The R lamp of the top group of lamps is now illuminated over back contact IIof relay R5, front contact E13 ci relay Rl and back contact i i9 of relay R8, and the Y lamp of the bottom group of lamps is illuminated over back contact l I of relay R5, front contact I io of relay Rl and back contact il? of relay so that signal CSi displays a restricting signal indication.

In the event the track section W-X is alrea occupied and the track circuit is shunted by t leading train, then no electromotive force is in duced in the windings 22 and 23 and the code following relays CFS and GF4 are inactive so that the decodingr relays ara all deenergized and released. Under this condition of the decoding relays, the R lamp of the top group of lamps is illuminated over back contacts H5, IIS and IIS of relays R5, Rl and R8, respectively. The lamp of the bottom group of lamps ls now illuminated over back contacts H2 and III of relays RB and R'i so that the signal CSI displays a slow speed signal indication.

It is to be pointed out that when the track circuit current impulses are of relatively large magnitude the first stage ampliier tube VTI of the apparatus of Fig. 2 and of the apparatus of Fig. 5 may be omitted and the primary winding 3U of transformer T2 connected directly with the inductor windings 22 and 23.

It is to be observed from the foregoing description of the apparatus of Fig. 5 that the most essential part of the electromotive force induced in the windings 22 and 23 by the current impulses of the track circuit is that part tending to drive the grid of tube VTZ or VT3 positive. When the polarity of the impulse is such that the grid of tube VT2 or VT3 is driven negative, the electroniotive force is of no use so far as the useful operation of the apparatus is concerned, and is in fact somewhat harmful. It follows, therefore, that the amplifier ahead of tubes VTZ and VT3 is most useful if arranged to amplify most strongly only that part of the incoming electromc-tive force that tends to drive the grid of tube VT2 or VT3 positive in potential with respect toi its filament. This advantageous condition is effected by the apparatus of Fig. 6.

Referring to the train cai` 1ied apparatus of Fig. 6, the amplifier ahead of the tube VTZ and VT3 comprises two tubes VT5 and VTS having their grid circuits connected to the secondary winding IZI of a transformer TII in a push-pull arrangement, the primary winding 22 of transformer TII being connected with the inductor windings 22 and 23. A resistor R9 is interposed in the grid circuit of tube VTB and a resistor Ri is interposed in the grid circuit of tube VT5. The plate circuit of tubes VT and VTS are connected with the generator 29 in parallel, a resistor I23 being interposed in the plate circuit of tube VTS and a resistor i213 being interposed in the plate circuit of tube VT5. The plate circuit of tube VTS is coupled with the grid of tube VTZ through a condenser CII, and the plate circuit of tube VI'5 is coupled with the grid of tube VT3 through a condenser CIZ. A control unit comprising a condenser CIS and a resistor |25 is connected between the grid and filament oi tube VTZ, and in like fashion a control unit comprising a condense:` C54 and a resistor [2G is connected between the grid and filament of tube VT3.l The code following relays CFB and GF4 of Fig. G are interposed in the plate circuit of tubes V'I2 and VT3, respectively, the same as in Fig. 5, and these code following relays govern the decoding relays R5, R6, Rl' and R8 in the saine manner as in Fig. 5. Also, the decoding relays of Fig. 6 govern the operating circuit for signal CSI, the same as in Fig. 5.

The parts are so proportioned that normally the grids of tubes VT?. nd VT3 are of substantialiy the same potential as the filaments of the tubes, and a relatively large steady value of plate current fiows in the respective plate circuits so that relays CFS and GF4 are both energized and picked up.

Assuming the train on which the apparatus of Fig. 6 is mounted is moving in the normal direction of traflic through the track section W-X of Fig. 4 under clear traffic conditions so that current impulses of positive polarity and of the code frequency of '75 cycles per minute are supplied to the track rails, an electroinotive force is induced in windings 22 and 23 which in turn induces an electroinotive force in the secondary winding I2I of transformer Ti I. The connections are so arranged that this electromotive force thus induced in the secondary winding 2l causes during the first half cycle of the wave form of the induced electromotive force the lower terminal of winding lil to be positive and the top terminal to be negative. I shall first consider the effect of tube VTi and the associated tube VT3 in response to this electromotive force thus induced in the secondary winding I2I. When the crest of the wave form of the electromotive force drives the grid of tube VTS positive in potential with respect to the associated filament, electrons are attracted to the grid so that grid filament impedance of tube VTS is lowered, which correspondingly lowers the total impedance of the grid circuit of tube VTS, with the result that the major portion of the impedance of the circuit is now found in the resistor RIG which is proportioned for relatively high Voltage resistance. Current iiows in the grid circuit and the voltage drop of resistor RIll accounts for the major portion oi tive, the plate current on tube VT5 is increased so that the voltage drop of resistor I24 is increased and the potential applied to the plate of tube VT5 is lowered since the voltage of the generator 29 remains constant. This decrease in the potential oi the plate of tube VTS is applied to the grid of tube VT3 through the coupling condenser CI2, the potential of the grid of tube VT3 being therefore rendered negative with respect to its filament. The plate circuit current of tube VT3 is in turn reduced. The reduction of the plate current of tube VT3 is small because the electromotive force is not amplified much by the tube VTS due to the large voltage drop in resistor RIU. The resultant reduction in the plate current of tube VT3 is not only relatively small but it lasts only for a short time because of the short duration of the current impulse of the track circuit, with the result that the code following relay CF4 is not released.

I shall now consider the effect of the induced electromotive force in secondary Winding I2| on the tube VT6 and its companion tube VT2. The grid of tube VT6 is rendered negative in potential with respect to its filament by substantially the full crest voltage of the first half cycle of the induced electromotive force because no current ows in the grid circuit of tube VT6. Hence there is a relatively large reduction in the plate circuit current of tube VT6. Since the voltage drop of resistor |23 is made smaller due to the reduction in the plate circuit current of tube VT6, the potential applied to the plate of tube VT6 is increased and a resultant potential of positive polarity is applied to the grid of tube VT2 through the coupling condenser CI I. With the grid of tube VT2 rendered positive in potential With respect to its filament, grid current flows in the grid circuit of tube VT2 and condensers CII and CI3 are charged thereby. The positive potential thus applied to the grid of tube VT2 causes a corresponding increase in the plate circuit current of that tube which in turn increases the energization of the relay CFS, and no operation of that relay is at this time effected. When the half cycle of the induced electromotive force ceases, condensers CII and CI3 apply a negative potential to the grid of tube VT2 during the time of its discharge through the resistor |25. The negative potential thus applied to the grid of tube VT2 causes a reduction in the plate current of tube VT2 suflicient to cause the release of relay CF3 since the reduction persists during the discharge of the condensers CII and CI3. Condensers CII and CI3 are discharged and the apparatus restored to its normal condition prior to the expiration of the code cycle interval. It is clear therefore that the code following relay CFS is operated for each impulse of the track circuit current. The control unit comprising condenser CI3 and resistor is so proportioned that substantially equal on and 01T periods in the operation of relay CFS are eiected. Since the code frequency of the track circuit current impulses is that of 75 cycles per minute, both relays R'I and R8 are picked up and the cab signal CSI displays a clear signal indication.

In the event approach restricting traiiic conditions exist so that the code of the track circuit current impulses of section W-X is that of negative polarity and 75 cycles per minute, the electromotive force induced in the secondary winding I2I is opposite in polarity to that previously described, and this time the top terminal of winding I2I is positive and its bottom terminal is negative. The positive potential thus applied to the grid of tube VT6 causes grid current to flow and the voltage drop of resistor R8 is large so that the resultant positive potential for the grid of tube VTS is not large and the resultant increase in the plate circuit current of tube VT6 is not large. Hence the negative potential applied to the grid of tube VT2 through condenser CII is not large and the resulting reduction of the plate current for tube VT2 is not suflicient to reduce the energization of that relay to a point where it releases, and the reduction lasts for only a brief interval. The negative potential applied to the grid of tube VT5 is ampliiied and causes a relatively large reduction in the plate circuit current of tube VTS, and a resultant large positive potential is applied to the grid of tube VT3 through condenser CI2. Grid current ilows for the tube VT3 and condensers CI2 and CI4 are charged thereby. At the expiratlon of the current' impulse the charge on condenser CIII renders the grid of tube VT3 negative with respect to its filament and the plate circuit current is reduced to a point where the relay GF4 is released, the reduction in the plate circuit current being effected for a rela.- tively long interval during the discharge of condensers CI2 and CI4 through the resistor |26. It follows therefore that the .relay GF4 is operated in response to each current impulse of the track circuit current and the decoding relays R5 and RB are picked up to cause the cab signal CSI to display an approach restricting signal indication.

In the event approach traffic conditions exist for the section W-X so that the code of the current impulses is that of negative polarity and a frequency of 50 cycles per minute, the action of the electron tubes is the same as described in connection with approach restricting traffic conditions except the code following relay GF4 is operated at therfrequency of 50 cycles per minute and relay R5 only is picked up, with the result that signal CSI displays an approach signal indication.

In the event'restricting traiiic conditions exist for` the section W-X so that the code of the current impulses is that of positive polarity and a freqency of 50 cycles per minute, the action of the electron tubes is the same as that described under clear traffic conditions except the code following relay CF3 is operated at the frequency of 50 cycles per minute and relay R1 only is picked up with the result that the signal CSI displays a restricting signal indication.

It is obvious that in the event the track section W--X is already occupied and the track circuit.

shunted, no electromotive force is induced in the windings 22 and 23 of Fig. 6 and the code following relays CF3 and CFII remain inactive and the decoding relays are all deenergized and released, with the result that the cab signal CSI displays a slow speed signal indication.

Although I have herein shown and described only a few forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. A signal system comprising, a transmitting circuit, means including a code transmitter operative at times to supply to said circuit successive current impulses of unidirectional current and the successive impulses of which are separated by an interval longer than the impulse interval, receiving means receiving energy from said circuit and effectively influenced by each such cur' rent impulse, a relay including a contact member which is moved to a selected position in response to a predetermined condition of energiaation of the relay for a predetermined interval, means including capacitance associated with said receiving means and with said relay to store up energy during each current impulse interval and to give up such energy during the interval between successive current impulses to eiect said predetermined condition of energication of said relay for said predetermined interval, and a signaling circuit controlled by said contact member.

2. A signal system comprising, a transmitting circuit, means including a code transmitter operative at times to supply to said circuit a signal current consisting of successive current impulses u l uenced by each such current impulse, an electromagnetic device, energy st ring means including capacitance, means to associate said energy storing means with said receiving means to store up energy in response to each of said current impulses, other means to associate said energy storing means with said electromagnetic device to effect energization of the device by the giving up of such stored energy during the interval between successive current impulses, and signaling means controlled by said electromagnetic device and operated to a selected position in response to such recurrent energization of the device.

3. A signal system comprising, a transmitting circuit, a source of unidirectional current, coding means operable to divide time into successive cycles or" a selected interval, means to connect said source to said circuit and controlled by said coding means to supply to said circuit a single effective surge of current each cycle the duration of which surge is relatively short and only a small portion of the cycle interval, receiving means coupled with said circuit effectively influenced by each such current surge, a relay governed by said receiving means and requiring for effective energization a period greater than the duration of such surge of current, a condenser, means to associate said condenser with said receiving means and with said relay to charge the condenser during each current surge and to effect by discharging said condenser during substantially the remaining portion of each cycle interval energization of said relay, and a signal circuit including a contact of said relay.

e. A railway signal system comprising, a track section, a code transmitter having an operation cycle of a selected interval and operating to continuously repeat such cycle, a source of unidirectional current, means controlled by said transmitter to connect said source across the rails of said section to supply to the rails during each operation cycle a single effective current impulse the duration or" which is relatively short and is only a small portion of the cycle interval, receiving means receiving energy irom the track rails and effectively influenced by each such current impulse, an electroresponsive means including a contact member normally occupying a irst position and operated to a second position in response to a predetermined change in the energization of the electroresponsive means, signaling means controlled by said contact member, and means including capacitance associated with the receiving means and with the electroresponsive means to receive a charge in response to each current impulse and to eiect said change in the energization of the electroresponsive means by discharging during the remaining portion of each cycle interval.

5. A railway signal system comprising, a track section having a track circuit, a code transmitter having an operation cycle of a selected interval and operating to continuously repeat such cycle, a track battery, traic controlled means cooperating with said code transmitter to supply from said battery to said track circuit during each said cycle a single effective surge of current of high peak voltage and short duration and which duration is only a relatively small portion of the cycle interval, receiving means receiving energy from the track circuit effectively influenced by each such current surge, slow acting relay controlled by said receiving means, a condenser, means to associate said condenser with said receiving means to charge the condenser during each current surge, other means to associate said condenser with said relay to cause energization of the relay during substantially the remaining portion of each cycle interval in response to the discharge of 'the condenser, and a signal circuit controlled by said relay,

6. A railway signa-l system comprising, a track section having a track circuit, a code transmitter having an operation cycle oi a selected interval and operating to continuously repeat such cycle, a track battery, traffic controlled means cooperating with said code transmitter to supply from said battery to said track circuit during each said cycle a single eflective surge of current of high peak voltage and short duration and which duration is only a relatively small portion of the cycle interval, receiving means receiving energy from the track circuit electively inuenced by each such current surge, a circuit controlling electromagnetic device governed by said receiving means and which device is characterized by requiring for effective energization a period greater than the duration of such surge of current, a condenser, means controlled by said receiving means for charging the condenser during each such current surge and for eiecting energization of said device during the remaining portion of each cycle interval by discharging said condenser, and a signal circuit controlled by said electromagnetic device.

7. A signal system comprising, a transmitting circuit, a quick acting code following relay having a contact member biased to a first position and operated to a. second position when the winding of the relay is effectively energized by a current impulse of a predetermined short duration, means to effectively couple the winding of said relay with said circuit, a condenser, a decoding relay which is picked up when ellectively energized for a relatively long period, a source of direct current, means including said Contact member at its second position to connect said condenser across said source to charge the condenser, means including said contact member at its iirst position to connect said condenser across the winding of said decoding relay to energize that relay by the discharge of the condenser, transmitting means including a code transmitter connected with said transmitting circuit and operative to supply at times recurrent current impulses which are of said predetermined short duration and are spaced apart by an interval substantially equal to said relatively long period to operate the code following relay for causing periodic energization of said decoding relay for said relatively long period, and

signaling means controlled by said decoding relay.

8. A signal system comprising, a transmitting circuit, a polar code following relay having a polar Contact member biased to a irst position and operated to a second position only when the winding of said relay is energized by current of a selected polarity, means to eirectively couple the winding of said relay with said circuit, a condenser, a decoding relay which is operated when energized for a relatively long period, a source of direct current, means including said contact member at its second position to connect said condenser across said source to charge the condenser, means including said contact member at its first position to connect said condenser across the Winding of said decoding relay to energize that relay by the discharge of the condenser, transmitting means including a code transmitter connected with said transmitting circuit and operative to supply recurrent current impulses of said selected polarity and short duration but which are spaced apart by an interval substantially equal to said relatively long period to operate the code following relay for periodically energizing said decoding relay for said relatively long period, and signaling means controlled by said decoding relay.

9. A signal system for railways comprising, a track section having a track circuit, a source of unidirectional current, tranic controlled coding means operative to divide time into successive cycles of a given interval and to supply under a given trafiic condition from said source to said track circuit a single effective current impulse during each cycle, said impulses all of one polarity and each impulse of only a relatively small portion of the cycle interval, a polar code following relay having a polar contact member biased to a first position and operated to a second position only when the winding of the relay is energized by current of a selected polarity, means to couple the winding of said relay with said track circuit as required for operation of said contact member -by each said current impulse, a condenser, a slow acting relay, means including the second position of said contact member to connect said condenser across a source of direct current to charge the condenser, means including the first position of said member to connect said condenser with the Winding of said slow acting relay to energize that relay by the discharge of the condenser, and signaling means governed by said slow acting relay.

10. A railway signal system comprising, a track section, a source of unidirectional current, traic controlled coding means operative to supply from said source to the rails of said section recurrent current impulses of one polarity under a first traic condition and recurrent current impulses of the opposite polarity under a second traffic condition, a first and a second code following relay each provided with a contact member biased to a first position and operated to a second position when the winding of the associated relay is effectively energized, means to couple the windings of said relays with the track rails of said section as required to effectively energize said first relay only by the current impulses of said one polarity and to effectively energize said second relay only by the current impulses of said opposite polarity, a first and a second condenser, a first and a second decoding relay, a source of direct current, means to connect said first condenser across said direct current source over the second position of the contact member of said first code following relay and to connect said second condenser across that source over the second position of the contact member of said second code following relay, means to connect said first condenser with the winding of said first decoding relay over the first position of the contact member of said first code following relay and to connect said second condenser with the winding of said second decoding relay over the rst position of the contact member of said second code following relay, and a signal having a first and a second indication selectively governed by said decoding relays.

11. A railway signal system comprising, a track section, trackway coding means operative atA times to supply to the rails of said section coded direct current of a given polarity, said coded current consisting of current impulses each of relatively high peak voltage and short duration and the successive impulses separated by an interval longer than the impulse duration, a train carried receiving circuit receiving energy from the track rails, a train carried electron tube provided with a plate circuit including a code following relay and having its grid circuit coupled with said receiving circuit as required to apply a positive potential to the grid in response to each of said current impulses, means for normally creating a negative bias on the grid of said tube to establish substantially zero plate current for effectively energizing said relay only during the interval energy is received by said receiving circuit in re-` sponse to each of said current impulses, a condenser and a slow acting decoding relay mounted on the train, means to connect said condenser across a source of direct current overa front contact of said code following relay to charge the condenser during each of said currentimpulses, means to connect said condenser with said decoding relay over a back contact of the code following relay to energize the decoding relay by the discharge of the condenser during each interval between successive current impulses, and a signal controlled over a contact of said decoding relay.

l2. A railway signal system comprising, a track section, trackway apparatus operative under one traffic condition toI supply to the rails of said section a first code current and under another traflic condition to supply to the rails a second code current, said coded currents each consisting of recurrent current impulses of relatively short duration with the impulses of the first code all of positive polarity and the impulses of the second code all of negative polarity, a train carried receiving circuit inductively receiving energy from the track rails and including the primary winding of an input' transformer, a first and a second electron tube having plate circuits with a first code following relay interposed in the plate circuit of the first tube and a second code following relay interposed in the plate circuit of the second tube, means to connect the grids of said tubes with a secondary winding of said transformer in a push-pull arrangement, a biasing battery interposed in the connection between the cathodes of said tubes and the center terminal of said secondary winding to create a negativebias for the grids of said tubes to eii'ect substantially zero plate circuit current, said transformer windings disposed so that the first half cycle of the electromotive force induced in the secondary winding in response to each rail current impulse of positive polarity renders the grid of said one tube positive in potential with respect to its cathode to cause plate current to flow for that tube and operate said first relay in step with the first code current and the first half cycle of the electromotive force induced in the secondary winding in response to each rail current impulse of negative polarity renders the grid of said second tube positive in potential with respect to its cathode to cause plate current' to flow for that tube and operate said second relay in step with the second code current, and train `carried decoding and signaling means selectively controlled by such operation of said code following relays.

13. A` railway signal system comprising, a track section, trackway apparatus operative under one trafc condition to supply to the rails of said section a first code current and under another traffic condition to supply to the rails a second code current, said coded currents each consisting of recurrent current impulses of relatively short duration with the impulses of the rst code all of positive polarity and the impulses of the second code all or" negative polarity, a train carried receiving circuit inductively receiving energy from the tracl: rails and including the primary winding of an input transformer, a rst and a second electron tube having plate circuits with a irst code following relay interposed in the plate circuit oi the first' tube and a second code following relay interposed in the plate circuit of the second tube. means to connect the grids of said tubes with a secondaryl` Winding of said transformer in a push-pull arrangement, a biasing battery interposed in the connection between the cathodes of said tubes and the center terminal of said secondary winding to create a negative bias for the grids of said tubes to eiect substantially Zero plate circuit current, said transformer windings disposed so that the rst half cycle of the electromotive force induced in the secondary winding in ren sponse to each rail current impulse of positive polarity renders the grid of said one tube positive in potential with respect to its cathode to cause plate current to low for that tube and operate said first relay in step with the rst code current and the first half cycle of the electromotive force induced in the secondary winding in response to each rail current impulse of negative polarity renders the grid of said second tube positive in potential with respect to its cathode to cause plate current to flow for that tube and operate said second relay in step with the second code current, train carried decoding and signaling means selectively controlled by such operation of the code following relays, and an auxiliary biasing unit including a condenser' and a resistor in multiple connected in series with said biasing battery.

i4. A signal system comprising, a iirst and a second polar code following relay each provided with a contact member biased to a first position and operated t'o a second position only when the winding of the associated relay is energized with current of a selected polarity, decoding means controlled over said contact inembers for selectively operating a signal, an electron tube, an output transformer, a plate circuit for said tube including a source of current and the primary winding of said transformer, a rst secondary winding of said transformer connected With the winding of said first relay and poled to operate that relay when an electromotive force of normal polarity is induced in that winding, a second secondary winding of said transformer connected with the winding of said second relay and poled to operate that relay when an electromotive force of reverse polarity is induced in that Winding, an input' transformer, a grid circuit for said tube including a winding of said input transformer, biasing means interposed in said grid circuit to establish a potential of the grid of the tube with respect to the cathode effective to cause a selected value of plate circuit current so that an increase in grid potential increases the plate current and induces in said secondary windings electromotive forces oi normal polarity to operate said irst relay and a decrease in grid potential decreases the plate current and induces in said secondary windings electromotive forces ol reverse polarity to operate said second relay, and transmitting means coupled with a winding of said input transformer for at times supplying recurrent current impulses of a polarity as required to increase the grid potential and for at other times supplying recurrent current' impulses of a polarity as rcquired to decrease the grid potential.

l5. A railway signal system comprising, a track section, a source of direct current, coding mea-ns for reversibly coupling said source with the rails of the sections to supply a rst or a second code current according to a first oi a second trai. c condition, said rst code current consisting of recurrent current impulses of relatively short duration and high peak voltage with the successive impulses separated by an interval longer than the impulse duration and the impulses all oi one polarity, said second current impulses consisting of such current impulses but all ol the opposite polarity, a train carried receiving circuit receiving energy from the track rails, a irst and a second electron tube having their grid circuits coupled with said receiving circuit in a push-pull arrangement and having their plate circuits arranged in parallel with a rst code following relay interposed in the plate circuit or the iirst tube and a second code following relay interposed in the plate circuit of the second tube, said gid circuits normally conditioned to create grid potentials substantially equal to that of the cathodes to produce -a steady value of plate current for each tube, a rst and a second control unit each comprising a condenser and a resistor in multiple, said rst unit interposed in the grid circuit of the first tube adjacent the grid of that tube and said second unit interposed in the grid circuit of the second tube adjacent the grid of that tube, said receiving and grid circuits poled as required to create a positive grid potential for the rst tube during each rail current impulse of said one polarity to cause grid current to flow to charge the condenser of said first unit and to create a positive grid potential for the second tube during each rail current inipulse of said opposite polarity to cause grid cui'- rent to flow to charge the condenser of said second unit, said condensers when thus charged effective to create a negative grid potential for the respective tube and to discharge through the associated resistor during the interval between successive rail current impulses to cause an operation of the associated code following rela-y, and decoding means selectively controlled by such operation of the code following relays.

16. A railway signal system comprising, a track section, a source of direct current, coding means for reversibly coupling said source with the rails of the sections to supply a first or a second code current according to a first or a second traliic condition, said first code current consisting of recurrent current impulses of relatively short duration and high peak voltage with the successive impulses separated by an interval longer than the impulse duration and the impulses all of one polarity, said second current impulses consisting of such current impulses but all of the opposite polarity, a iii-st and a second electron tube mounted on a train having grid circuits of a push-pull arrangement and plate circuits with a iirst code following relay interposed in the plate circuit of the rst tube and a second code iollowinfr relay interposed in the plate circuit of the second tube, said grid circuits normally conditioned tc create grid potentials effective to produce -a steady value of plate current for each tube, a rst and a second control unit each cornprising a condenser and a resistor in multiple, said first unit interposed in the grid circuit of the first tube adjacent; the grid of that tube and said second unit interposed in the grid circuit of the second tube adjacent the grid of that tube, train carried receiving means to inductively couple said grid circuits with the track rails and so arranged as to create positive grid potential for the first tube by the first half cycle of the electromotive force induced in the grid circuits by each current impulse of said first code current to charge the condenser of said rst unit and to create positive grid potential for the second tube by the first half cycle of the electromotive force induced in the grid circuit by each current impulse of said second code current to charge the condenser of said second unit, said condensers when thus charged to create a negative grid potential for the respective tube and to discharge through the resistor of the same unit during the interval between successive impulses of code current to cause operation of the associated code following relay for each impulse of the code current, a slow acting decoding relay for each code following relay effectively energized when the respective code followingr relay is operated. and signaling circuits: selectively governed by the decoding relays.

1'7. A railway signal system comprising, a track section, a source of direct current, coding means for reversibly coupling said source with the rails of the sections to supply a first or a second code current according to first or a second traffic condition, said first code current consisting of recurrent current impulses of relatively short duration and high peak voltage with the successive impulses separated by an interval longer than the impulse duration and the impulses all oi' one polarity. said second current impulses con- Sistine: of such current impulses but all of the opposite polarity, a first and a second electron tube mounted on a train having grid circuits of a push-pull arrangement and plate circuits with a first code following relay interposed in the plate circuit of the first tube and a second code following relay interposed in the plate circuit of the second tube, said grid circuits normally conditioned to create grid potentials effective to produce a steady value of plate current for each tube. a flrst and a second control unit each comprising a condenser and a resistor in multiple, said first unit connected across the grid and cathode of the first tube and said second unit connected across the grid and cathode of the second tube, a train carried receiving circuit inductively receiving from the track rails in response to each current impulse of said code currents an electromotive force the first half cycle of which tends when the current is of the first code to create a positive potential for the grid of the first tube and a negative potential for the grid of the second tube and tends when the current is of the second code to create a positive potential for the grid of the second tube and a negative potential for the grid of the rst tube, amplifying means interposed between said receiving and grid circuits effective to amplify at high gain only that portion of such electromotive forces that tends to create positive potential for said first or second tube, said first control unit effective in. response to such recurrent periods of positive grid potential for the first tube to create negative grid potential during the interval between such recurrent periods to cause operation of the first code following relay in step with the first code current, said second control unit effective in response to such recurrent periods of positive grid potential for the second tube to create a negative grid potential during the interval between such recurrent periods to: cause operation of the second code following relay in step with the second code current, and decoding means selectively controlled by such operation of the code following relays.

18. In combination with a section of railway track, a reactance device including a Winding mounted on a magnetic core and a condenser, means to connect a portion of said winding across the track rails to form an oscillatory track circuit for said section, a source of unidirectional current, means to periodically connect said source to said device to store up energy therein and to periodically disconnect said source from said device to cause current of a damped wave to flow in said circuit, and a relay connected with said rails effectively energized by such current wave.

19. In combination with a section of railway track, a track relay connected across the rails at one end of the section, a reactance device including a winding mounted on a magnetic core and a condenser connected across said winding, means to connect a selected portion of said winding across the rails at the other end of said section, said reactance device so proportioned as to form an oscillatory track circuit for said section, a source of unidirectional current, and means to periodically connect said source with said device to store up energy therein and to periodically disconnect said source from said device to cause current of a damped wave to flow' in said track circuit to effect substantially the same average energization of the track relay for both dry and wet ballast conditions.

20. In combination with a section of railway track, a track relay connected across the rails at one end of the section, a reactance device including a winding mounted on a magnetic core anda condenser connected across said winding, means to connect a selected portion of said winding across the rails at the other end of said section, said reactance device so proportioned as to form an oscillatory track circuit for said section, a source of unidirectional current, and means to periodically connect said source with said device to store up energy therein and to periodically disconnect said source from said device to supply to said track circuit current impulses having high peak voltage and a damped wave to effect when the section is unoccupied substantially the same average energization of the track relay under all weather conditions and to break down the rail film resistance as an aid to shunting when the section is occupied.

21. In combination with a section of railway track, a track relay connected across the rails at one end of the section, a reactance device including a winding mounted on a magnetic core and a condenser connected across said winding, means to connect a selected. portion of said winding across the rails at the other end of said section, Vsaid reactance device so proportioned as to form an oscillatory track circuit for said section, a source of unidirectional current, and means to periodically connect said source with said device to store up energy therein and to periodically disconnect said source from said device to supply to said circuit current impulses of high peak voltage and a damped Wave to effect when the section is unoccupied substantially the same average energization of the track relay under all weather conditions and to cause when the section is occupied by a train a current surge of relatively high amperage as an aid in inductively transferring energy to signaling apparatus carried on the train.

22. In combination with a section of railway track, a polar track relay having its winding connected across the rails at one end of the section and having its armature biased for operation only in response to current of a selected polarity owing in its winding, a reaotance device including a winding mounted on a magnetic core and a condenser connected across said winding, means to connect a portion of said winding across the rails at the other end of said section to form an oscillatory track circuit for said section, a source of unidirectional current, and means to periodically connect said source with said device to store energy therein and to periodically disconnect said source from said device to cause current of a damped wave to now in said track circuit and the first half cycle of which current wave is of said selected polarity to operate the armature of the track relay when the section is unoccupied and is of relatively high peak voltage to effect when the section is occupied by a train a current surge of relatively high amperage to aid in inductive transfer of energy to train carried signal apparatus.

23. In combination with a section of railway track, a track relay having its winding connected across the rails at one end oi' the section and having a contact member biased to a first position and operated to a second position in response to energization of its winding, means including a code transmitter connected across the rails at the other end of the section to supply to the rails recurrent current impulses for periodically energizing the winding of said track r-elay, a condenser, a slow acting decoding relay, a source of direct current, means including said contact member at its second position to connect said condenser across said source to charge the condenser, and means including said contact inember at its first position to connect said condenser across the winding of said decoding relay to eilectively energize the decoding relay in response to the recurrent current impulses supplied to the track rails.

24. In combination, a iirst and a second track section, means including a source of unidirectional current and a coding mechanism` connected to the rails at one end of said iirst section and operative to supply current of Iour different codes for four diiierent traiic conditions respectively, said irst code consisting of current impulses of positive polarity and a first code irequency, said second code consisting of current impulses oi negative polarity and said first code frequency, said third code consisting oi current impulses of negative polarity and said second code frequency and said fourth code consisting of current impulses of positive polarity and said second code frequency, a first and a second polar code following relay each provided with contact members biased to a first position and operated to a second position only when the winding of the associated relay is energized by current of a selected polarity, means to connect the windings of said relays with the rails of said first section so that said iirst relay is operated by current impulses of positive polarity and said second relay is operated by current impulses of negative polarity, a slow release control relay controlled over a contact member of said first relay, another source of unidirectional current; circuit means connected to tne rails of said second section and including said other source, pole changing contacts of said control relay and a contact member of each of said rst and second code following relays to supply to the rails of the second section current impulses of the same code as supplied to the rails of the first section; and receiving and decoding means connected to the rails of the second section selectively responsive to said four different codes.

WILLARD P. PLACE.

lll 

